The thickness of a layer produced during the construction of a road should be measured continuously and, if possible, in real time. Because the requirements with regard to the precision of the paving dimensions are relatively high in practice, it is not sufficient if the plane is recorded at a place in front of the screed and combined directly with a rear edge of the screed for the thickness of the produced road pavement, because this fails to take into consideration unevennesses of the plane.
In practice, systems are known that determine the thickness of the road pavement by means of direct measurement, for example, by means of ultrasound or radar. The disadvantage in this case, however, is that to some extent, reflective bodies must be employed for an exact measurement of the thickness of the road pavement in order to be able to locate the boundary layer precisely.
In another method for determining the layer thickness of a newly produced road pavement, measurement bodies are slid into a newly laid layer. This, however, can result in substantial damage to the newly laid pavement.
A further known approach provides for storage and combination of the values measured on the plane, whereby a reference is used in order to connect all values to one another.
In practice, the layer thickness is also calculated using an inclination sensor. This is described, for example, by DE 100 25 462 A1. This document discloses a device for determining the thickness of the paving layer on the basis of a predetermined distance between the position of a height sensor and the screed rear edge, the registered height above the subgrade and a determined tow arm-screed assemblage inclination, which is determined by means of an inclination sensor.
The use of inclination sensors, however, has the technical disadvantage that these are susceptible to all sorts of accelerations and therefore lead to an imprecise measurement result. In particular, the inclination sensors are disturbed during their measurement by shaking or by vibrations transferred to the screed assemblage. Small errors in the inclination sensors thereby cause large errors in the calculation of the layer thickness.
It is likewise problematic if a large number of distance sensors is needed to faithfully reproduce the surface of the plane, because all measured values of the sensors must be connected to one another in order to create a suitable reference. This method is complicated and additionally requires expensive equipment in order to determine the suitable reference.
In practice, external references are also used in order to determine the layer thickness of a newly laid road pavement. The external references are thereby positioned or mounted alongside the road paver. This is impractical, however, because either the complete section must first be provided with such references or the references must be moved at regular distances in order to allow a continuous determination of the layer thickness.
DE 100 25 474 A1 describes a device for determining the layer thickness of a laying material to be applied to a subgrade by a road paver, whereby the road paver has a tractor, at least one tow arm mounted rotatably on the tractor in a manner that allows the height to be adjusted, a floating screed rigidly attached to the at least one tow arm that, with the tow arm, forms a tow arm-screed assemblage and an undercarriage lying with its bottom side on the base. The device furthermore comprises a distance sensor attached in a stationary manner to the tractor, for measuring a relative distance between a reference position of the tractor and a reference position of the tow arm-screed assemblage, whereby the reference position of the tractor has a predetermined positional relationship to the bottom side of the undercarriage, and the reference position of the tow arm-screed assemblage has a predetermined positional relationship to a lower back edge of the screed.
DE 198 51 153 C1 relates to a method for measuring a driving surface, in which the driving surface profile is registered metrologically. Here, a driving surface is, in particular, a traffic area, e.g. a street or a highway, that is set up with a number of coats or layers in the framework of highway construction or repair work. The invention furthermore relates to a system for carrying out the method with a mobile testing device.
EP 0 510 215 B1 describes a device for regulating a driving surface cover thickness. The device comprises height sensors and inclination sensors, all of which are arranged on a screed assemblage in such a way that they follow a movement of the screed.
U.S. Pat. No. 7,172,363 B2 refers to a paving machine. The paving machine can have a power source, a traction system, a hopper that is configured to hold paving material, and one or more conveyors that are configured to transfer the paving material from the hopper. The paving machine can also have a plate or a screed board that is configured to lay out a mat of the paving material. The paving machine furthermore comprises at least one front sensor that is mounted on a front part of the paving machine and configured in order to measure the height from a surface to the front sensor, and at least one rear sensor that is mounted on the paving machine and configured in order to measure the height from a surface of the mat to the rear sensor. The paving machine also comprises a controller that is configured to determine a thickness of the mat by determining a difference between one or more front height measurements that have been recorded by at least one front sensor, and one or more rear height measurements that have been recorded by the at least one rear sensor. The sensors are mounted on a support that is permanently connected to the screed.
Although the use of inclination sensors mentioned at the beginning is not problem free, it would likewise not be reasonable to disregard the inclination reference generated in this way on an uneven subgrade, because doing so would make it impossible to carry out an exact measurement of the layer thickness of the road pavement.